A pair of isomeric saponins with cytotoxicity from Albizzia julibrissin

Two new saponins have been isolated from the stem barks of Albizzia julibrissin Durazz, and their structures identified as 3-O-beta-D-xylopyranosyl-(1 --> 2)-beta-D-fucopyranosyl-(1 --> 6)-beta-D-2-deoxy-2-acetoamidoglucopyranosyl]-21-O-{(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-4-O-((6S)-2-trans-2-hydroxymethyl-6-hydroxy-6-methyl-2,7-octadienoyl)-beta-D-quinovopyranosyl]-2,7-octadienoyl}-acacic acid-28-O-beta-D-glucopyranosyl-(1 --> 3)-alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl ester (1) and 3-O-beta-D-xylopyranosyl-(1 --> 2)-beta-D-fucopyranosyl-(1 --> 6)-beta-D-2-deoxy-2-acetoamidoglucopyranosyl]-21-O-{(6S)-2-trans-2-hydroxymethyl-6-methyl-6-O-3-O-((6S)-2-trans-2-hydroxymethyl-6-hydroxy-6-methyl-2,7-octadienoyl)-beta-D-quinovopyranosyl]-2,7-octadienoyl}acacic acid 28-O-beta-D-glucopyranosyl-(1 --> 3)-alpha-L-arabinofuranosyl-(1 --> 4)]-alpha-L-rhamnopyranosyl-(1 --> 2)-beta-D-glucopyranosyl ester (2), based on chemical and spectral evidences, named as julibroside J19 and julibroside J18, respectively. Both compounds show significant inhibition action against HeLa, Bel-7402 and MDA-MB-435 cancer cell lines in vitro.